Updating UBOS fails with lots of error messages containing "Unrecognized archive format"

You probably haven’t updated your Device for a long time. In the meantime, we have started distributing some packages with a new, faster, compression scheme, and your version of pacman and dependent libraries are too old to recognize it. So upgrade pacman and libarchive first.

First, find the cached pacman and libarchive packages on your system:

% find /var/cache/pacman -name pacman-\* -or -name libarchive\*

Then, if the names of the found files are, for example, /var/cache/pacman/pkg/pacman-5.2.1-4-x86_64.pkg.tar.zst and /var/cache/pacman/pkg/libarchive-3.4.1-1-x86_64.pkg.tar.zst, copy those files locally and uncompress them:

% cp /var/cache/pacman/pkg/pacman-5.2.1-4-x86_64.pkg.tar.zst .
% cp /var/cache/pacman/pkg/libarchive-3.4.1-1-x86_64.pkg.tar.zst .
% zstd -d pacman-5.2.1-4-x86_64.pkg.tar.zst
% zstd -d libarchive-3.4.1-1-x86_64.pkg.tar.zst

Then, install the uncompressed files:

% sudo pacman -U pacman-5.2.1-4-x86_64.pkg.tar libarchive-3.4.1-1-x86_64.pkg.tar

and proceed as you regularly would with updating UBOS.